1. Field of the Invention
The present invention relates to a technique for miniaturizing semiconductor integrated circuits. The invention disclosed in this specification includes in its scope an element formed using a compound semiconductor, in addition to an element formed using a silicon semiconductor, as a component of a semiconductor integrated circuit, and relates to a semiconductor device manufactured using an oxide semiconductor as an example and a manufacturing method of the semiconductor device.
In this specification, a semiconductor device generally means a device which can function by utilizing semiconductor characteristics, and an electrooptic device, a semiconductor circuit, and electronic device are all semiconductor devices.
2. Description of the Related Art
In recent years, semiconductor devices have been developed to be used as an LSI, a CPU, or a memory. A CPU is an aggregation of semiconductor elements each provided with an electrode which is a connection terminal, which includes a semiconductor integrated circuit (including at least a transistor and a memory) using a semiconductor wafer.
A semiconductor circuit (IC chip) of an LSI, a CPU, or a memory is mounted on a circuit board, for example, a printed wiring board, to be used as one of components of a variety of electronic devices.
Silicon-based semiconductor materials are widely known as semiconductor materials that can be used for a transistor in a semiconductor circuit. For example, in Patent Document 1, a structure in which the distance between a channel formation region and a contact portion is shortened to reduce the resistance generated therebetween is proposed for higher integration.
Oxide semiconductors have been attracting attention as materials other than silicon. For example, in Patent Document 2 and Patent Document 3, a technique by which a transistor is manufactured using zinc oxide or an In—Ga—Zn-based oxide as an oxide semiconductor and is used as a switching element or the like of a pixel of a display device.